1. Field of the Invention
The present invention relates to a washing solution for washing an ink jet head of art ink jet recording device, to a method for producing the washing solution, and to a method for washing an ink jet head using the washing solution.
2. Description of the Related Art
The principle behind the ink jet recording method is to jet either liquid or molten solid ink from a nozzle, slit, porous film, or the like so as to perform a recording on paper, cloth, film, or the like. Various methods are proposed for jetting ink. These methods include a so-called charge control method of jetting ink. by making use of electrostatic induction force, a so-called drop-on-demand pressure pulse method of jetting ink by making use of the vibration pressure of a piezoelectric element, and a so-called thermal ink jet method of jetting ink by making use of the pressure produced by forming and growing air-bubbles under high temperatures. An extremely fine image can be produced by these methods.
Well-known inks used in the ink jet recording method include aqueous dye inks produced by dissolving various aqueous dyes in a liquid medium composed of water and an aqueous organic medium, aqueous pigment inks produced by dispersing various pigments in a liquid medium composed of water and an aqueous organic medium, and oil dye inks produced by dissolving an oil-soluble dye in an organic medium. Among these inks, the aqueous ink is highly safe because its major medium is water and is hence the dominant ink used in ink jet recording.
In order to use such an aqueous ink for ink jet recording, if it is stored in an ink jet recording head, the ink must have the characteristics that it is stably held in the head in the liquid form and it prevents clogging caused by drying, changes in ink compositions caused by drying and deterioration in an image caused by the changes, and leakage. In contrast, the ink must have the reciprocal characteristics that it penetrates and is dried and fixed promptly when printed onto a printing medium such as paper.
In order to obtain such an ink that penetrates and is dried and fixed promptly while preventing clogging in the ink jet head, there have been attempts based on the ink composition to add a humectant, penetrant, thickener, and the like, thereby balancing both characteristics. Because the aqueous ink uses water as its major medium, it dries naturally and it is difficult to avoid the problem of clogging caused by drying when the ink is stored for a long period of time and in high temperature and low humidity conditions.
In order to solve such a problem, there have been various proposals including a method for storing an ink jet print head stably and a method for washing a head clogged during storage or the like.
For example, Japanese Patent Application Laid-Open (JP-A) No. 60-139454 discloses a method for long-term storage for a head. This method, however, has, for example, the problem that a storage liquid is mixed with ink during storage. This requires a jetting operation using a large amount of ink when the head is first reused.
JP-A No. 6-8461 discloses a method for washing a clogged head. This method, however, has the problem that because only a small amount of washing solution is used, it has an insufficient washing effect on hardened clogging. Also, bubbles tend to be created, especially on the surface of a water-repellent nozzle, which adhere to the nozzle and are not removed by washing. Moreover, the adoption of this type of structure having no relation to the jetting performance of ink gives rise to the problem of a complicated device.
JP-A No. 61-144357 also discloses a washing method. In this method, however, the flow of the washing solution does not uniformly spread over the entire surface of the nozzle with the result that some parts of the surface of the head are not washed.
A method is proposed in JP-A No. 4-115954 in which a washing solution comprising an organic solvent, surfactant, and water is sprayed onto the surface of ahead. This method, however, has an insufficient washing effect on hardened clogging with aqueous ink.
In this manner, there is a demand for measures to recover from clogging with ease.
The manufacturers fill an ink jet head with ink to perform printing inspection prior to its delivery and deliver the ink jet head after the ink is removed and the head is washed. After the head is delivered, it is exposed to stressful conditions such as long-term storage in the market. This can cause clogging and printing defects occur in an early stage after the start of its operation. This is caused by the washing solution which remains unremoved in the head after the ink is removed and the head is washed.
Therefore, there is a demand for means to maintain an ink jet head in a normal condition even when it is not used but stored for a long period of time.
In view of this, there have been various proposals on washing solutions and washing methods for an ink jet head when aqueous ink is used.
For instance, a washing method using a washing solution having a coefficient of viscosity lower than ink is disclosed in JP-A No. 63-260451. A washing solution comprising water, an organic solvent, and a surfactant is proposed in JP-A No. 4-115954. A washing method using a washing solution of a highly alkaline solution or surfactant solution is disclosed in JP-A No. 6-8471.
Even if these washing solutions and washing methods are used, however, the residue obtained after washing is finished, where these washing solutions contain a highly viscous material, coagulates into a highly viscous material which causes clogging in the fine flow passage of an ink jet head and adheres to a nozzle face whereby printing defects tend to be caused. When the washing solution is a highly alkaline solution, a highly concentrated alkaline material adheres to the head and corrodes the head material, when the residual washing solution dries in the nozzle. In addition, because no disinfectant/germicide treatment is performed, the viable cell number in the washing solution is large. Therefore, the residual washing solution remaining in the ink jet head is deteriorated imparting an adverse effect. Also, the washing solution is deteriorated during long-term storage.
JP-A No. 58-71170 proposes a method for discharging the washing solution using air after ink is replaced with a washing solution. This method has an object of preventing clogging derived from the deteriorated washing solution residue and the like.
However, even if the washing solution is discharged from the ink jet head and the head is stored in an empty condition, the residue remaining unremoved causes the same problems as above.
Accordingly, an object of the present invention is to provide an ink jet head washing solution which restores a print head, which has caused problems such as clogging and the like, to its normal condition and maintains the print head in a normal condition when it is stored at high temperature or for a long period of time, thereby maintaining a high image quality, to provide a method for producing the washing solution, and to provide a method for washing an ink jet head.
Another object of the present invention is to provide a method for effectively washing an ink jet print head, the print head having a nozzle whose surface is ink-repellent, the method having a high degree of efficiency and being capable of easily restoring a print head suffering from the problem of clogging, for example, to its normal condition without using a complicated device.
The present inventors directed their attentions to the solubility of an evaporation residual component in ink which component caused clogging in the ink jet head and to a residual component giving rise to clogging and printing defects after being washed. The residual component after being washed includes a large amount of substances with a viscosity of 10 mPas or more at 25xc2x0 C., substances which were solid at 25xc2x0 C., and substances derived from a fungous proliferation and the residual component causing clogging could be dissolved in a basic polar solvent with low viscosity such as water and lower alcohol. The present invention was thus completed.
According to a first aspect of the present invention, there is provided a washing solution for an ink jet head of an ink jet printer which prints using an aqueous ink, the washing solution comprising 80% by weight or more of water and 1.0% by weight or less of a substance with a viscosity of 10 mpas or more at 25xc2x0 C. and/or of a substance which is a solid at 25xc2x0 C., the viable cell number in the washing solution being 0.5/ml or less, wherein the washing solution has a viscosity between 0.6 and 3.0 mpas at 25xc2x0 C. and an electroconductivity between 3xc3x9710xe2x88x922 and 3xc3x9710xe2x88x925 S/m.
The washing solution according to the first aspect of the present invention and a method for washing an ink jet head using this washing solution can protect an ink jet head from accidents caused by a leakage of ink and drying under stressful conditions, e.g. high temperature storage, long-term storage, strong impact, and atmospheric pressure reduction and stably maintains a print image quality the same as before these stresses are applied. The washing solution according to the first aspect of the present invention is also low in viscosity and high in solubility. Hence even if there is clogging caused by the strong precipitation and fixing of an ink component onto the nozzle surface of the ink jet head, the washing solution easily penetrates into fine gaps between precipitates, whereby the precipitated component can be dissolved. Therefore, the ink jet head whose nozzle suffers from clogging can be restored to its normal condition in an extremely simple manner by the washing solution and the method for washing an ink jet head using the washing solution.
If the maker performs such a washing and delivers an ink jet head after a printing inspection is finished, the reliability in the market is improved. Where an ink jet head is expected to be exposed to severe stressful conditions, such a washing operation avoids the situation which gives rise to problems such as a deterioration in image quality. Further, ink jet heads suffering from problems such as clogging caused by stresses in the market can be restored with ease.
The forgoing is primarily for the explanation of the washing of an ink jet head using the washing solution. The present invention has an additional effect. In the washing of an ink jet head, maintenance parts are washed at the same time. In printers which are used by customers copying a considerable number of sheets or which have been used for approximately five years, maintenance parts, e.g. the wiper for cleaning a nozzle surface, nozzle cap parts, the suction maintenance pump, and the passage to the waste ink absorber may be operating in an abnormal manner due to the adherence of ink. Even in this case, the maintenance unit can be restored to its normal condition by washing the head and the maintenance parts at the same time using the method for washing an ink jet head by using the washing solution of the present invention.
The present inventors also found that the above second object could be achieved by dipping a nozzle face in a washing solution containing water as a major component in the washing of an ink jet head which prints by jetting an aqueous ink from a nozzle having a water-repellent surface.
According to the second aspect of the present invention, there is provided a method for washing an ink jet print head which prints by jetting an aqueous ink from a nozzle having a water-repellent surface, the method comprising a step of dipping a nozzle face of the print head in a washing solution